1. Field of the Invention
The invention relates to a method of controlling the temperature of intake air which is provided from outside air through an air-feed system. The invention also relates to a temperature-control device for carrying out the method and a gas turbine having the temperature-control device.
In many plants, in particular in internal-combustion engines or compressors, an air feed may be necessary for operation. To that end, an air-feed system which provides intake air obtained from outside air is normally provided. Such an air-feed system may include, for example, a number of intake elements as well as filter elements.
In a gas turbine as well, it is necessary to feed intake air to a compressor which is connected upstream of a combustion chamber. To that end, such an air-feed system is normally likewise connected upstream of the compressor. The air drawn in by the air-feed system is generally accelerated when flowing through the air-feed system. In the process, that acceleration may be effected locally on one hand while flowing around or through an obstacle, for example a bird protection grille or a filter. On the other hand, however, an approximately adiabatic acceleration of the drawn-in air also results from a constriction of the cross section of flow along the throughflow path in the air-feed system. That adiabatic acceleration of the drawn-in air is associated with an enthalpy reduction. The enthalpy reduction in turn produces a temperature drop in the drawn-in air. It is established mathematically, for example, that the drawn-in air cools down by about 5.degree. C. during an acceleration of the drawn-in air to a velocity of about 100 m/s, which is normally present at the inlet of the compressor of the gas turbine. Ice may form in the process depending on the state of the outside air, in particular its pressure and temperature. That formation of ice may lead to a reduction in output of the gas turbine, to breakdowns, or even to damage to the gas turbine and is therefore to be avoided.
In order to avoid the formation of ice in the intake air provided by the air-feed system of the gas turbine, it is normal practice to warm up the intake air before it enters the compressor of the gas turbine or at the inlet of the air-feed system. In that case, conventional heating systems or anti-icing systems are used. In such a heating system, the intake air may be heated up by various methods such as, for example, by feeding recirculated hot compressor air, by using a steam-heated heat exchanger or even by using electric heating. Similar systems for preventing the formation of ice in the intake air provided by an air-feed system may also be used in other plants, such as, for example, in internal-combustion engines or compressors.
However, the use of a heating system results in a consumption of thermal energy, which is then no longer available to the gas turbine or the plant. Thus the efficiency of the gas turbine or the plant is reduced by the use of such a heating system.